Troubleshooting

CIRCUIT DESCRIPTION
The ECM compares the waveform of the oxygen sensor located before the catalyst with the waveform of the oxygen sensor located after the catalyst to determine whether or not catalyst performance has deteriorated.
Air-fuel ratio feedback compensation keeps the waveform of the oxygen sensor before the catalyst repeatedly changing back and forth from rich to lean.
If the catalyst is functioning normally, the waveform of the oxygen sensor after the catalyst switches back and forth between rich and lean much more slowly than the waveform of the oxygen sensor before the catalyst.
But when both waveforms change at a similar rate, it indicates that catalyst performance has deteriorated.






DETECTING CONDITION

CONFIRMATION ENGINE RACING PATTERN





(1) Connect LEXUS hand-held tester to DLC3, or connect probe of oscilloscope between terminals OXL1, OXL2, OXR1, OXR2 and E1 of ECM.
(2) Start engine and warm it up with all accessories switched OFF until water temperature is stable.
(3) Race engine at 2,500 3,000 rpm for about 3 minutes.
(4) After confirming that waveforms of heated oxygen sensors bank 1, 2 sensor 1 (OXL1, OXR2), oscillate around 0.5 V during feedback to ECM, check waveform of heated oxygen sensors bank 1, 2 sensor 2 (OXL2, OXR2).

HINT: If there is a malfunction in system, waveform of heated oxygen sensors bank 1, 2 sensor 2 (OXL2, OXR2) is almost same as that of heated oxygen sensors bank 1, 2 sensor 1 (OXL1, OXR1) as shown.

There are some cases where, even though a malfunction exists, MIL may either light up or not light up.





WIRING DIAGRAM

INSPECTION PROCEDURE